The present invention generally relates to the field of X-ray imaging systems such as computed tomography (CT) systems and more particularly to a method and apparatus for focusing and bending of electron beams in an X-ray tube.
X-ray imaging systems, such as CT systems, operate by projecting fan shaped or cone shaped X-ray beams through an object. The X-ray beams are generated by an X-ray source, and are generally collimated prior to passing through the object being scanned. The attenuated beams are then detected by a set of detector elements. The detector elements produce a signal based on the intensity of the attenuated X-ray beams, and the signals are processed to produce projection or tomographic images.
Conventionally, in certain imaging systems such as CT systems, the X-ray sources and detectors may be disposed on a circular rotatable gantry such that the X-ray sources and X-ray detectors are radially opposed 180 degrees from each other. Hence, rotation of the gantry enables angular fanning of an X-ray beam around the body so that the attenuated X-ray signals are angularly detected by the rotating X-ray detectors to produce an image. To eliminate mechanical complexities associated with rotating gantries, such as in CT systems, some imaging systems have employed stationary X-ray sources and detectors disposed circumferentially about an object to be imaged. Accordingly, absent any rotation of the X-ray sources, these systems employ alternate means for fanning or manipulating the X-rays around the body so that proper angular coverage of X-rays is obtained and, consequently, a reliable image of an object can be produced.
Currently, stationary CT systems employ X-ray sources or X-ray tubes having controllable electron beams (e-beams) steered onto a target for producing X-rays along various angles. However, controlling the electron beams of such systems typically requires use of magnetic fields to divert and focus the e-beam as desired. Unfortunately, forces produced by magnetic fields may have slow response times in manipulating the e-beam, which may be insufficient to produce images with desired quality. Further, systems employing magnetic fields tend to be big in size and high in cost rendering them less desirable for vendors to purchase.
Therefore, there is a need for stationary X-ray tubes producing e-beams which can be steered and focused readily and quickly. There is also need for X-ray tubes which are compact reliable and cost effective.